1. Field of the Invention
This invention relates generally to deflection systems in a charge particle recording apparatus. The invention relates more particularly to deflection systems requiring a high degree of deflection accuracy and to an improved method and apparatus for enhancing the scanning linearity of a charged particle beam in a recording apparatus and for improving the geometric fidelity of the reproduced image.
2. Description of the Prior Art
A scanning charged particle beam is often used to produce an image with informational content. Various well-known uses include television receivers, video displays, recording devices and the like. An image recorded by a scanning charge particle beam is not precisely reproduced, but rather is subject to distortions resulting from various factors including those introduced by the scanning beam reproduction device itself. Distortions can result from drive signal distortion, variations in construction of deflection yokes and electrostatic plates, variations in orientation and position of yokes and deflection plates, variations in electron guns, etc. While the quality of image reproduction is sufficiently high to satisfy the needs of many such uses, certain applications of charged particle scanning systems require that beam scanning be conducted with substantially reduced distortion in order to attain a desired relatively high fidelity in reproduced image information. An electron beam recording system utilized to reproduce geophysical information in connection with petroleum field exploration is an example of one such application requiring relatively high fidelity in a reproduced image.
Various techniques have been employed to reduce distortions which are introduced into the reproduced image by the beam scanning device itself. The distortions principally comprise geometric and other distortions which are revealed by distortions in the reproduced image. Such distortions are unacceptable in applications requiring high geometric fidelity.
It is known in prior linearity correcting arrangements, to generate a correction signal in order to reduce distortion. However, such prior art does not provide the relatively high degree of linearity desired for certain applications. Moreover, those circuit arrangements provided for producing the correcting signal have multiple adjustments, many of which are interactive thus requiring repeated readjustment and causes the set-up of the scanning system to be a laborious, tedious and costly procedure.
In another linearity correcting arrangement, a diode matrix is utilized which provides a relatively large number (e.g., 81) of matrix intersections at which voltage deviations are determined. Adjustments are made to a large number of potentiometers which are coupled in circuit with the diodes to cause the beam to more accurately scan a linear trace. While this arrangement provides some degree of linearity correction, the numerous potentiometers are interactive and must be repeatedly readjusted. This adjustment is substantially time consuming, tedious and costly.